Estersil-thickened lubricating composition modified with hydrogen-bonding donor compound, and process of making



nited States 2,746,922 ESTERSE-THICKENED LUBRICATING COMPOSE- TION MODIFIED WITH HYDROGEN-BONDING DONOR COMPOUND, AND PROCESS OF MAK- ING No Drawing. Application June 4, 1952, Serial No. 291,897

Claims. (Cl. 2252-28) This invention relates to novel lubricating compositions and processes for making them, and is more particularly directed to compositions and processes in which the rheological properties of lubricants comprisig an estersil and a Water-insoluble lubricating oil are controlled by mixing therewith a hydrogen-bonding compound.

Estersils are a novel class of materials disclosed and claimed in United States application Serial No. 171,759, filed July 1, 1950, by Ralph K. Iler, now abandoned, and in Iler, United States Patent 2,657,149, issued October 27, 1953, on application Serial No. 315,930, filed October 21, 1952, as a continuation-in-part of said application Serial No. 171,759. More particularly, an estersil is an organophilic solid in a supercolloidal state of subdivision, having an internal structure of inorganic siliceous material with a specific surface area of at least 1 m. g. having chemically bound to said internal structure-OR groups wherein R is a hydrocarbon radical, wherein the carbon atom attached to oxygen is also attached to at least 1 hydrogen, each OR group having from 2 to 18 carbon atoms. In United States application Serial No. 191,717, filed October 21, 1950, by Ralph K. Iler, and issued April 20, 1954, as United States Patent 2,676,149, lubricating compositions comprising a Water-insoluble lubricating oil and an estersil of an inorganic siliceous material having a specific surface area of at least 25 m. g. are disclosed and claimed.

Control of the rheological properties of lubricants is necessary to adapt the lubricants for use under the Widely varying conditions and requirements commonly encountered. This means that control must be exercised over the response of the rheological properties of the lubricant, such as consistency and apparent viscosity, to such variables as temperature, prevailing humidity, and shear force. For instance, a grease for a roller bearing to be used under extreme loading may desirably be relatively thick as applied to the bearing and thin out to a mobile liquid under the operating conditions in order to permit proper feeding of the lubricant. Conversely, in the lubrication of an automobile chassis it is desirable that the grease show little change in permanent consistency in order to permit maximum retention.

Further, it is desirable that a lubricant retain its original rheological properties after storage, in order that it will perform as designed.

Now according to the present invention I have found that the rheological properties of lubricants comprising a Water-insoluble lubricating oil and an estersil may be controlled by incorporating therein a hydrogen-bonding electron donor compound in which no electron donor atom is attached to two different silicon atoms. In a preferred aspect of the invention I have found that by mixing polyfunctional hydrogen-bonding donor compounds such as water, ethylene glycol, and glycerine, With a Water-insoluble oil, such as a hydrocarbon oil, and an estersil I can improve the thickening efiiciency of the estersil and produce a grease which has a substantially more constant atent consistency upon storage under humid conditions. In a further preferred aspect, I have found that by adding a hydrogen-bonding donor compound such as tricresyl phosphate and di-n-butyl ether, in Which the donor atom has a relatively Weak tendency to donate electrons, to lubricants comprising a hydrocarbon oil and an estersil, i can reduce the tendency for such lubricants to form agel-like mass upon storage at elevated temperatures. In a still further preferred aspect, by adding a monofunctional hydrogen-bonding donor compound, such as stearyl alcohol, I can prepare stable dispersions of estersils in hydrocarbon oils, such dispersions being particularly useful because of their improved viscosity index.

The control of rheological properties according to my invention is advantageous in estersil-modified lubricants generally, as in slightly modified lubricating oils, oils modified to an extent desirable for hydraulic fluids, and oils thickened with estersils to make greases. The effects are particularly Well illustrated in greases and hence the invention will be described With especial reference to greases, although it will be understood that the descriptions given are more broadly applicable to other lubricants also.

The advantages of controlling the rheological proper ties of greases according to my invention are manifested in unexpected and unobvious Ways. For instance, improved corrosion resistance of materials lubricated With greases of rheologically controlled properties is an unexpected consequence of the application of my invention.

I have observed that certain estersil-thickened greases have a tendency to harden between intermittent periods of use and when in this hardened condition, the film formed by such a grease is rather easily cracked and broken. Corrosive agents such as air and moisture are enabled to reach the metal surface through such cracking and thereby corrode it. Through proper rheological control effected by adding a hydrogen-bonding donor compound, especially the polyfunctional-type compounds, I am able to reduce substantially such hardening and consequently minimize film failure and resultant corrosion.

Reduced gelation characteristics of estersil-thickened greases modified with relatively weak electron donor compounds according to the invention results in improved feeding characteristics When such greases are used for lubricating roller-type anti-friction bearings. This advantage is particularly noticeable When such bearings are used under high loads.

The advantage of using a monofunctional hydrogenbonding donor compound for controlling rheological properties of a lubricating oil is especially pronounced in situations where a relatively minor proportion of an estersil is used to improve the viscosity index of a lubricating oil. For instance, by adding the monofunctional hydrogen-bonder, stearyl alcohol, to a dispersion of 2% of an estersil in a hydrocarbon oil, I can maintain a satisfactory suspension of the estersil in the oil over a considerably increased period of time.

Other important advantages of rheological control according to my invention are observed when estersil-thickened greases are used in combination with other agents commonly encountered under conditions of practical operation. Thus, When bearings may be lubricated alternately with conventional soap-thickened greases and with greases thickened With an estersil, consistency changes in the estersil-thickened grease may occur, and I am enabled to control such changes by the addition of suitable hydrogen-bonding donor compounds. Similarly, various conventional additives are used to impart particular properties to lubricating oils and greases made from such lubricating oils, and by the use of suitable hydrogenbonding donor compounds I am able to control the rheological properties of the resultant mixtures as desired for particular uses.

To understand fully the nature of my improvement in lubricating compositions one must first understand the nature of the component constituents of the compositionsnarnely, the estersil, the lubricating oil, and the hydrogen-bonding donor compound. These will now be individually described.

THE ESTERSIL Estersils suitable for use in the compositions of the present invention may be prepared by esterifying an inorganic siliceous material having a specific surface area of at least 1 m. g. with a primary or secondary alcohol in which the hydrocarbon radicals have from 2 to 18 carbon atoms, as described in the above-mentioned application Serial No. 171,759. While the siliceous material which acts as a substrate for the estersil may have a specific surface area of as little as 1 m. /g., it is preferred to use estersils in which the substrate has a specific surface area of at least 25 m. g.

To make an estersil one takes a substrate of particles larger than colloidal size having a surface of silanol (SiOH) groups and esterifies it under substantially anhydrous conditions with a primary or secondary alcohol having from two to eighteen carbon atoms in its structure. The substrate thus acquires a coating of -OR groups bound to the silica surface, and since the alcohol used was primary or secondary, the particular atom in the R chain attached to the oxygen atom will also necessarily be attached to at least one hydrogen atom. The substrate particles are of such a size and character that they have a specific surface area of at least one square meter per gramthat is, either the individual particles are solid, dense, siliceous material so finely divided that the surface area is in this range, or the particles are larger but so porous that the surface area is thus extended.

Suitable substrates for making into estersils may be in any of a wide variety of forms. Although the surface must be silica, the substrate need not be silica throughout its structure, and materials, upon the surface of which silica has been deposited or otherwise eifected to be present, are entirely suitable. Particles of clay, talc, asbestos, mica, and other silicate minerals, for instance, have some surface silanol groups and may be esterificd to form estersils, or the proportion of surface silanol groups may be increased by depositing amorphous silica thereon or by treating the silicates with an acid, such as sulfuric, to dissolve out metal ions and leave more silanols.

Preferred as substrates for some uses, however, are amorphous silica products, especially porous, coherent aggregates of ultimate, amorphous silica particles. Silica gel has such a structure and may be used as a substrate.

The esterification of a silica in the form of very small,

discrete particles having a gel structure within the particles was described in application Serial No. 590,728, filed April 27, 1945, by Ralph K. ller, now abandoned. Open-pored substrates of this general type, wherein the pores have an average diameter of at least four millimicrons, can be esterified and then dried, preferably from an organic liquid, to give estersils which are very porous and easily crushed by mechanical action. The structure of the aggregates in the substrate may be reinforced, prior to esterification, by mixing them with an aqueous dispersion of active silica and heating above 60 C. at a pH of 8 to 11, whereby the active silica accretes to the aggregates, as described in application Serial No. 99,354, filed June 15, 1949, now abandoned, by Alexander, Iler and Wolter.

The ultimate silica units in the aggregates of substrate need not be the 2 to 5 millimicron particles present in a conventional silica gel. Rather, they may be builtup particles, such as those of the Bechtold and Snyder Patent 2,574,902, issued November 13, 1951. For instance, a sol prepared by ion exchange as described in Bird Patent 2,244,325 may be heated above 60 C. and further quantities of the same type of sol may be added with continued heating until at least five times as much silica has been added as was originally present, whereby the ultimate silica particles are built-up into the size range of 15 to 130 millimicrons. These particles may be coalesced, as by adding a long-carbon-ehain nitrogen compound as described in ller application Serial No. 99,355, filed June 15, 1949, now Patent No. 2,663,650. Alternatively, ultimate silica units may be built up in the presence of salts by adding an acid, such as sulfuric, to a sodium silicate solution above 60 C. at a sodium ion normality not over one, over a period of time, as described in Iler copending application Serial No. 65,526 filed December 5, 1948, now abandoned, or by adding to a silica sol above 60 C. a silicate solution and enough acid to maintain the pH at from 8 to 11, and continuing the additions until the ultimate units have reached the desired size, as described in application Serial No. 99,350, filed June 15, 1949, now Patent No. 2,601,235, by Alexander, Her and Wolter.

The alcohol used for esterifying the substrate may be any primary or secondary alcohol having at least two carbon atoms. The alcohol may be straightor branched-chain, or alicyclic, saturated or unsaturated, alkyl or aromatic. Examples of alcohols which may be used are: ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, ndecyl, n-undecyl, n-dodecyl, n-tetra-decyl, n-hexadecyl, n-octadecyl, isobutyl, isoamyl, 2,2,4-trimethyl hexane-l-ol, 5,7,7,-trimethyl 2-octanel-ol, isopropyl, sec-butyl, sec-amyl, secn-octyl, methyl iso-butyl carbinol, di-iso-propyl carbinol, cyclopentanol, cyclohexanol, cycloheptanol, menthol, allyl, crotyl, oleyl, citronellol, geraniol, propargyl, benzyl, beta-phenylethyl, hydrocinnamyl, alpha-methylbenzyl, and cinnamyl.

To effect esterification, the alcohol is heated with the substrate under substantially anhydrous conditions. Water formed by the reaction is removed, as by azeotropic distillation. Usualy an excess of the alcohol over that theoretically required is employed, and the water content of the alcohol at the end of the reaction period should not exceed about 5% for maximum esterification. The rate of reaction increases as the temperature is raised, suitable temperatures to give the indicated type of product in a one-hour reaction time being as follows:

The esterified products are organophilic in that in a two-phase n-butanol-water system, for instance, they prefer to be wet by the butanol. When sufficiently esterified they are hydrophobic--that is, are not readily wetted by water. When estcrificd to the maximum de gree, they are impervious to methyl red dye and do not adsorb it from anhydrous benzene solution. The -OR groups in the estersils are chemically reacted with the silica surface and cannot be removed by washing with hot methyl ethyl ketone or similar solvents, or by prolonged cxtraction in a Soxhlet extractor. No alcohol is displaced from the silica by treatment with solvents.

The properties of estersils are related to the number of ester groups per unit surface area of the substrate. Although the surface-modifying characteristics of different OR groups varies considerably, an estersil is generally organophilic when there are present on the surface more than about 100 ester groups per 100 square millimicrons of substrate surface area. When this proportion is 200 or more ester groups per 100 square millimicrons of substrate area the products are generally hydrophobic, and when it is 270 or more, the products do not adsorb methyl red dye from anhydrous benzene solution. On an unknown estersil the OR group can be identified by decomposing the estersil with acid to release the alcohol, and identifying the alcohol by usual analytical methods. The substrate surface area can be measured by burning off the ester groups in a stream of oxygen at 500 C.

THE LUBRICATING OIL The oils used in making the novel compositions of this invention are water-insoluble lubricating oils. Oils which contain, say, to of a water-soluble component or which are themselves soluble to that extent in water can be classed as essentially water-insoluble oils. However, to obtain maximum advantages of the water resistant properties of the estersils used according to this invention, the oil should have as low a solubility in water as possible and preferably should not be soluble in water to the extent of more than about 1%.

A wide variety of oils can be used. In general, any water-insoluble animal, vegetable, or mineral oil or synthetic chemicals having typically oily characteristics and lubricating or friction-decreasing properties can be used.

Illustrative of suitable water-insoluble lubricating oils are: hydrocarbon oils such as naphthene base oils, paraffin base oils, and petrolatum; silicone oils, such as the dimethyl siloxane linear polymers; fluorocarbon oils such as the perfluorinated petroleum oils; vegetable oils such as cotton seed oil and castor oil; animal oils such as sperm whale oil, lard oil, blow fish oil and degras; and water-insoluble synthetic chemicals having typical oily characteristics such as di(Z-ethyl hexl) adipate, bis-nonyl glutarate, di(Z-ethyl hexyl) thiopropionate, di(Z-ethyl hexyl) oxydibutarate, propylene oxide-tetrahydrofuram copolymer, di(Z-ethyl hexyl) sebacate; and dimethyl cyclohexyl phthalate.

The choice of a water-insoluble lubricating oil to be used is, of course, based on a consideration of the requirements of the field of application of the finished product. The considerations are analogous to those weighed in selection of an oil to be used with conventional soap thickeners. For example, illustrative of matters to be considered in choosing an oil for a given use are cost, maximum and minimum service temperature, oxidation stability, power consumption during bearing operation, chemical reactivity, and bearing enclosure design.

Thus, low cost would be a reason for choosing a petroleum oil of natural origin. Such oil is suitable for most common uses where extreme conditions are not encountered. If low temperature operation were desired, then low pour point, low viscosity, naphthene base petroleum oils, or synthetic di-ester, or polyether type oils would be favored. For high temperature operation, on the other hand, oxidation resistant and high viscosity oils would be suggested. Fluorocarbon oils should be considered where the product is to be used in corrosive chemical surroundings. Low viscosity oils are favored for use in bearings where low power consumption is desired and conversely high viscosity oils are favored where there are high bearing pressures. Tacky compositions obtainable thru the use of very high viscosity oils are used where there is poor mechanical enclosure of bearings.

THE HYDROGEN BONDER According to the present invention a hydrogen-bonding donor compound is added to an estersil-lubricating oil composition of the type just described to elfect control of the rheological properties of the mixture.

Hydrogen-bonding donor compounds are a well recognized group of chemical compounds having a certain electronic configuration. Hydrogen-bonding is a concept advanced in recent years to explain certain abnormalities in the chemical and physical behavior of mixtures of compounds one of which contain hydrogen attached to a strongly negative radical and the other an atom capable of donating a pair of electrons to form a directional or coordination bond. Since the bond is formed by the donation of an electron pair from one atom, the donor, to the other atom, the acceptor, the bond is not of the type conceived of as an ordinary valence bond but many of the properties of the mixture indicate that a real association between the donor and acceptor molecules has occurred. These mixtures, for instance, exhibit an abnormal vapor pressure lowering, that is, a deviation from Raoults law. There is further observed abnormal heats of mixing and abnormal deviation in viscosity and freezing point lowering.

It will be observed that the hydrogen-bonding donor compounds which are effective in the compositions of the present invention do not necessarily function exclusively by reason of their character as hydrogenbonding donor compounds. Certain classes such as amines, ethers, esters and amides probably function as donors because they contain a strongly electronegative atom which is capable of donating an electron pair to the hydrogen of a silanol group which may be present on the surface of an estersil. On the other hand, some of the electron donor compounds such as water, organic hydroxy compounds and carboxylic acids are capable of acting also as electron acceptors in that they contain a hydrogen capable of accepting an electron pair and such an electron pair may be donated from the oxygen of a surface silanol or siloxane group on the estersil particle. Suflice it to say that the compounds which by conventional methods can be shown to be electron donors in the usual sense of the word are effective according to the present invention. It may be further observed that some of the most highly efiective electron donor compounds in the compositions of the present invention are those which are capable of also acting as electron acceptors.

It seems quite likely that such compounds as water, alcohols, and carboxylic acids may function both as donor and as acceptor compounds in view of their high degree of eifectiveness. In any event it is believed that these materials would not function as acceptors to the exclusion of their function as donors.

From the above description it will be apparent that hydrogen-bonding donor compounds as a class may be used in the estersil-lubricating oil compositions of the present invention. The donor compound may be organic and of this group the ethers, amides, ketones, esters of phosphorus oxy-acids, and alcohols, as disclosed in Robinson United States Patent 2,392,767 may be employed.

If in a compound an atom capable of acting as an electron donor is attached to two different silicon atoms, as for example the siloxane oxygens of the polysiloxane or silicone oils, the compound has effects other than control of rheological properties when added to an estersil-oil composition. Hence, if the siloxane oxygens of the silicone oils are considered to make these oils hydrogen-bonding donor compounds, such compounds are beyond the scope of the present invention and not included therein.

More particularly, donor compounds which are especially effective for controlling rheological properties in a manner which will increase the thickening efiiciency of the estersil and minimize hardening of the grease upon storage are polyfunctional compounds. Such polyfunctional compounds may be selected from the group consisting of polyhydroxy compounds such as ethylene glycol, glycerine, pentaerythritol, sorbitol, mannitol, dextrose, resorcinol, 4,4'-dihydroxy diphenyl, ricinoleyl alcohol, decamethylene glycol, 1,3-propanediol, and propylene glycol; polyfunctional amines such as hexamethylene diamine and decamethylene diamine; polybasic acids such as oxalic, succinic, and azelaic; amino alcohols such as triethanol amine, 2-amino-2-methyl-1,3 propane diol, and orthoand para-amino phenol; alpha-amino carboxylic acids such as aspartic acid; hydroxy carboxylic acids such as IZ-hydroxy stearic acid, 9-, 10-, l2-hydroxy stearic acid, and lactic acid; and other polyfunctional hydrogenbonding donor compounds.

Particularly desirable to control rheological properties so as to reduce the tendency for gelation to occur are hydrogen-bonding donor compounds selected from the group consisting of phosphoric and phosphorous acid esters such as tricresyl phosphate, tributyl phosphate, and tributyl phosphite; oxyand thio-ethers such as di-n-butyl ether, Lorol methyl sulfide, dodecyl di-phenyl ether, Lorol sulfide, di-phenyl ether, and ethyl propyl sulfide; fatty acid esters such as stearyl palmitate, and sorbitan monooleate; condensation products of aromatic aldehydes such as benzoin; and other relatively weak hydrogenbonding donor compounds.

Particularly desirable for controlling rheological proper-ties so as to partially or completely peptize the thickening structure of the estersil to cause the lubricating compositions to lose consistency in a controlled manner or to prepare stable dispersions of estersils in lubricating oils or hydraulic fluids, are hydrogen-bonding donor compounds from the class consisting of monofunctional alcohols such a stearyl alcohol, cetyl alcohol, and hydroabietyl alcohol; monofunctional amines such as dodecyl amine, octadecyl amine, and Lorol amine; monofunctional amides such as stearamide; certain metal salts of carboxylic acids such as zinc laurate, aluminum stearate, lead oleate and lead naphthenate, and monoglyceridcs such as monoglyceryl stearate.

Water is a specifically preferred hydrogen-bonding donor compound for use in the present invention. It acts in a manner similar to ethylene glycol, glycerine, and other polyhydrated compounds described above. it is, of course, unique in its structure in that its atomic configuration permits it to act readily either for donating a pair of electrons from the oxygen of the water to the hydrogen of a surface silanol on the estersil, or for accepting a pair of electrons from the oxygen of a surface silanol or siloxane group in the estersil through the hydrogen of the water. Furthermore, water can act as a bridging agent in that the behavior just described can take place within a grou of water molecules. Thus, the water can act in the same manner as a difunctional alcohol and cause an increase in the thickening efficiency of the estersil. The

grease so produced also has substantially more constant I consistency upon storage under humid conditions and as a consequence permits improved rust prevention.

It will be apparent that mixtures of ditlerent hydrogen bonders may be employed in a grease and that depending upon the character of the individual bonders a combination of results can be effected. Thus, a mixture of equivalent amounts of octadecyl amine and a dibasic acid are quite effective in increasing the rust prevention characteris tics of the grease without an accompanying loss of water resistance.

Conversely, even when a single hydrogen bender is employed, the bonder may have a combination of properties some of which are desirable and others of which are either only tolerable or definitely undesirable. Thus, it is preferred to use hydrogen-bonding donor compounds which are nearly neutral, since acids or bases tend to reduce the water resistance of the estersil-lubricating oil compositions.

Similarly, it is preferred to use compounds which are not too volatile-that is, compounds boiling above about 60 C. at atmospheric pressure in order that the effectiveness of the bender may be retained after prolonged storage of the lubricant. For instance, diethyl ether is a hydrogenbonding donor compound, but it is so volatile that its use would present problems during storage.

Again, it is preferred, in general, to employ as hydrogenbonding donors, compounds which have a relatively high proportion of functional groups in proportion to the total molecular weight. Thus, water having a molecular weight of 18 contains at least 1 and potentially 3 functional groupsthat is, groups capable of donating a pair of electrons or accepting a pair of electrons and is hence highly etfective in small proportions. On the other hand, decamethylene diol, for instance, contains 2 functional groups at opposite ends of a 10 carbon chain and hence a larger weight percentage of the latter compound would be required to produce the same effect as a given proportion of water.

The hydrogen-bonding donor selected should be one which in the proportions used forms a homogeneous mixture with the estersil-oil composition. The mixture should be free of undispersed particles of the hydrogen-bonding donor compound. Thus, preferably the bonder is a liquid or is soluble in the oil to give a liquid product. In some instances, homogeneity may be achieved by heating the mixture of oil and hydrogen-bonder to elevated temperatures. Accordingly, a prospective hydrogen-bender is not ruled out for lack of homogeneity in the mixture until it has been tested in the mixture at elevated temperatures.

Lubricants of controlled rheological properties are made according to the present invention by mixing the estersil, the lubricating oil, and the hydrogen-bonding donor compound. Any means adapted to provide effective mixing under the conditions present in the three-component system may be employed.

The mixing can be carried out in milling and mixing devices of the kind used heretofore for introducing other non-soap thickeners into oil. Paint mills, ink mills, colloid mills, ball mills, homogenizers, mixers of the sigmaarm type, and similar devices can be used to give the desired thorough dispersion of the estersils in the oil. Provision for heating during mixing may be made. The type of milling or mixing device used to carry out the dispersion depends upon the physical and chemical characteristics of the particular estersil employed. Thus, an ink mill gives very good results in most cases, whereas a homogenizer which produces high shearing forces gives maximum dispersion and thickening efliciency particularly in the thinner greases. The power requirements of the mixing operation are low, especially with estersils having an amorphous silica substrate because of the organophilic character and porous pulverulent structure of the estersils.

It should be noted that, especially in the case of greases, the milling will be so intensive as to cause some break-up of the structure of the estersil. If the estersil is composed of aggregates or agglomerates of dense, ultimate particles, such aggregates of agglomerates may be broken down into the ultimate units or groups of them such as chains, rods, or sponge-like networks. Such milled fragments are, of course, still estersils since they contain surface silanol groups esterified with primary or secondary alcohols.

The proportions of estersil, lubricating oil and hydrogen-bonder in a composition of this invention may be widely varied depending upon the properties desired in the finished product. For lubricating compositions, the lubricating oil is the predominant component and the estersil and hydrogen-bender are minor components as to proportions. The estersil is highly elfective as a thickening agent for the lubricating oil to make greases, a surprisingly small proportion of estersil being sufficient for this purpose. The exact proportion of an estersil re quired to thicken a lubricating oil is discussed in the above-mentioned Iler application Serial No. 191,717.

The proportion of estersil used as a thickening agent depends upon such factors as the character and viscosity of the oil, the nature of the thickened oil desired, and the nature of the estersil itself.

The thickening efiiciency of an estersil is determined.

by a number of factors, such as particle shape, interaction of the surface of the particles with the oil, interac tion of the particles with each other, and the ability of the particles to immobilize a film of oil around themselves. Specific surface area is one of the most important factors. Kind and degree of esterification must be considered also.

Elongated particles are more efiicient thickeners than spherical ones. Such elongation exists in fibrous or platelike particles or may be achieved by the joining together or reticulation of ultimate spherical units. Particles consisting of networks of such reticulated ultimate spherical units in which the pore diameter is greater than about 4 millimicrons are also particularly effective thickeners. The smaller the ultimate spherical units forming the network, the more complex the labyrinth obtainable and the more oil which can be immobilized by a given Weight of thickener. Thus it is observed that, other factors being relatively constant, the thickening efliciency is im-- proved markedly as the unit particle size decreases as indicated by increased specific surface area. Thickening efiiciency decreases somewhat as longer chain ester groups are used and also as the substrate is more completely esterified.

In general, using estersils having a specific surface area of 25 to 100 m. g. esterified according to the preferred embodiments of the invention, from 20% to 40% by Weight of estersil is required to give a medium grease consistency with Mid-Continent solvent treated petroleum oil. In contrast, the same grease consistency is obtained with the same oil using from 8 to 25% by Weight of those estersils, similarly esterified, having substrate specific surface areas of 200 to 400 mP/g.

In the light of the above principles, one skilled in the art will be able to determine by a simple trial or two the amount of a given estersil needed to do the thickening job desired. In general, compositions of the invention are obtained by mixing oil and estersil in an oilzestersil weight ratio in the range of 200:1 to 0.1:1. Preferred grease compositions of the invention are obtained by using the preferred estersils having an amorphous silica substrate in an oil-estersil weight ratio of 16:1 to 3:1.

The estersil particles can be present in the compositions of the invention in the same form as that in which they were added to the lubricating oil. Also, they can be present as smaller particles resulting from milling of the estersil with oil so as to break up, at least in part, the coherent aggregate structure of the particles. In general, in the mixing and milling operation, the estersil particle size is reduced, as required, to avoid lumpiness. In the case of grease preparation, for example, the estersil structure is broken down and dispersed in the oil to the point where the grease is not lumpy and is unctuous to the touch. The grease compositions begin to feel rather smooth when the gross diameter of the estersil particles is less than about 150 microns. However, since such large particles are merely coherent aggregate of smaller utimate units, they are usually greatly reduced in size during the milling operation. Thus, in the case of the preferred estersils based on a precipitated amorphous silica substrate having a surface area of at least 200 mfl/g. and a pore diameter greater than 4 millimicrons, milling will reduce the aggregate to units smaller than 5 microns.

The nature of the esterified siliceous component of the oil-estersil compositions of the invention can be determined by first extracting the oil from the composition with a solvent and then analyzing the remaining esterified siliceous solid to determine its carbon content, identity of the ester groupings, and such properties as surface area, pore size, ultimate particle size, bulk density, and the like.

The term grease as used herein to refer to estersil-oil compositions of the invention means that the compositions have a consistency within the range conventionally 10 ascribed to greases heretofore, namely, a micro-penetra tion value of from 30 to 420 at 77 F. as determined by the method described in ASTM Standards on Petroleum Products and Lubricants, November 1949, page 1309.

When it is desired that the final product of the present invention be a viscous fluid rather than a grease the proportion of estersil employed will be less than that used for the thickening of the lubricating oil to a grease.

The proportion of hydrogen-bender employed may also be widely varied depending upon the properties desired in the final product and upon the character of the lubricating oil and estersil used. Generally, the hydrogen-bonding compound is not the preponderant component of the mixture but is, rather, a minor component. The precise proportion of bonder to use in any particular composition can readily be determined by adding various increments and determining the rheological control effected in the final product, the additions being discontinued when the desired properties are reached.

To explain the foregoing observations as to the effect of hydrogen-bonding donor compounds upon the rheological properties of estersil-oil compositions I have evolved a theory which while it appears to fit the facts is not to be construed as limiting the scope of the present invention, such scope being limited only by the claims appended hereto. It is my theory that upon the siliceous substrates of the esterils there are patches of silanol and/ or siloxane groups due either to incomplete esterification or to partial break-down of the estersil structure occurring when it is milled into the oil, or to both of these factors.

Such unprotected areas or patches are capable of interacting, as by hydrogen-bonding, with each other, with components of the mixture, or with moisture from the air. Now, the more of these interactions which occur among the estersil particles, either directly or indirectly through a polyfunctional hydrogen-bonding donor compound such as glycerine, the more complex will be the labyrinth of the solid estersil phase and the more oil will be entrapped therein. This will have the effect of increasing the thickening efliciency of the estersil or increasing the consistency or apparent viscosity of the lubricating composition at a given estersil concentration. The polyfunctional hydrogen-bonder such as glycerine appears to act as a bridge.

On the other hand, if the patches interact with a hydrogen-bonding donor compound which is monofunctional, or is difunctional but incapable of acting as a bridge, such as monoglyceryl stearate, interactions between estersil particles will be reduced or eliminated and this will result in a peptization or decrease in the thickening effect of the estersil phase.

Whether or not the foregoing theory is correct, it forms a basis upon which particular hydrogen-bonding donor compounds can be selected to afford the desired rheological properties. The application of the considerations just discussed is shown with reference to particular com positions in the examples given hereinafter.

Except for the fact that they have controlled rheological properties, the compositions of the present invention, in general, have properties similar to the estersil-oil compositions of the above-mentioned Iler application, Serial No. 191,717 and are useful for the same purposes, such usefulness being enhanced by the control of the rheological properties.

The products of the invention range from slightly viscous fluids thru greases to hard wax-like solids depending on the proportions and types of estersil and lubricating oil used in their preparation. In general, the greater the amount of a given estersil present, the thicker and firmer the composition.

The products appear completely homogeneous upon examination with the unaided eye or under a light microscope. No grit is visible. Often, especially when the pre- 11 ferred estersils having an internal structure of amorphous silica are used, the products are clear and transparent, thus, having improved appearance over conventional oilmetal soap greases and the usual opaque mixtures of lubricating oil and inorganic fillers.

The grease compositions of the invention have a buttery texture if the oil used in the composition is of moderate or low viscosity. With relatively high viscosity oils, say around 2000 SUS at 100 F., greases having a more tacky mixture are obtained.

The grease-like, and the semi-solid compositions of the invention are particularly characterized as being substantially non-melting, even up to temperatures at which the lubricating oil phase will ignite.

The grease compositions of the invention also possess excellent shear stability. This is illustrated by the fact that there is little or no change in their consistency as determined by the ASTM micropenetration method after working in such devices as the Hain microworker described in Naval Research Laboratory Report TP2817, April 1946, A Microworker for Lubricating Greases, by G. M. Hain.

The excellent lubricating properties and lack of grittiness or abrasiveness of the grease products of the invention have been demonstrated in wear tests in comparison with conventional soap greases using standard machines such as the Almen, Timken, and Cornell testers.

The lack of corrosive nature of the estersil greases is shown by rust prevention tests described in the examples.

The grease compositions of the invention are useful for those lubricating purposes for which greases have been used heretofore and have many advantages as will be apparent from the foregoing discussion and from the specific examples which follow. The invention is not limited to greases however. Estersils are used to particular advantage in increasing the viscosity index of water insoluble lubricating oils. The resulting products are useful as pressure transfer media and hydraulic fluids under varied temperature conditions because of their excellent stability and body. The products of the invention, especially the thickened grease-like materials, are useful for application to metal surfaces to provide protective coatings and films against corrosion.

The invention will be better understood by reference to the following illustrative examples in addition to those already given.

Example 1 A siliceous substrate was prepared as follows:

One volume of a solution of 0.48 N sulfuric acid was added at a uniform rate over a period of 30 minutes, at a temperature of about 30 C., to three volumes of a solution of sodium silicate containing 2% SiOz and having a molar SiOzzNazO ratio of 3.36:1. The sulfuric acid solution was chemically equivalent to 80% of the NazO in the sodium silicate solution. Vigorous agitation was provided to insure complete and instantaneous mixing and the temperature of the reacting mass was maintained below 40 C. thruout. During the acid addition, the pH dropped from 11.3 to about 9 and the sodium ion concentration remained below 0.3 N thruout the process. A clear sol resulted.

The sol obtained by the above step contained 1.5% SiO-z. The solids in the sol consisted of discrete particles of silica having an average diameter less than 5 millimicrons, too small to be measured by the electron microscope.

The sol was heated to 95 C. Solutions of sodium silicate and sulfuric acid were added simultaneously at a uniform rate over a period of two hours. The sodium silicate solution added contained SiOz and had a molar SiOzzNazO ratio of 3.36: 1. The sulfuric acid was a 4% aqueous solution and was added in amount sufficient to neutralize 80% of the NazO in the silicate solution. The addition of silicate and acid was continued until one part of SiOz had been added for each part of 12 SiO2 present in the initial sol. During the additions, vigorous agitation was employed. The pH of the mixture slowly rose from 9 to 10 during the additions and was then maintained at about 10. The sodium ion concentration remained below 0.3 N thruout the process.

During the heating of the initial sol and the subsequent addition of silicate and acid, the tiny discrete dense ultimate particles of silica increased in size; they became chemically bound together in the form of open networks or coherent aggregates of supercolloidal size. This action is called the build-up step. The aggregates precipitated so that the resulting mass was in the form of a slurry.

To aid filtration, the slurry was further fiocculated with a 2% solution of a mixture of cetyl and lauryl trimet'hyl ammonium bromide, 0.16% of the mixed compounds being added, based on the weight of the silica. The slurry was filtered and the wet filter cake reslurricd in water. The reslurry was adjusted to about pH 7 with dilute sulfuric acid, then filtered, and the filter cake washed with water. The undried filter cake as obtained on a vacuum filter contained about 12.5% SiOz by weight. The specific surface area of a sample of this substrate material, after drying in air at 120 C., was approximately 300 M. g. as measured by the aforementioned nitrogen adsorption method.

The esterification of the substrate was carried out as follows:

Twenty-two hundred grams of the wet filter cake containing about 275 grams of silica was slurried in 6 liters of n-butanol. The slurry was placed in a 12-liter, threenecked flask equipped with an electric heating mantle, a thermometer, a mechanical stirrer, and a three-quarter inch column three feet long, packed with fii-inch glass helices.

The slurry was heated and material allowed to distill at a refiux ratio of about 2:1 until the distillate no longer separated into two layers and the pot temperature had risen to above 116 C. indicating that most of the water had been removed by azeotropic distillation. The heating and distillation requiredabout 13 hours.

The slurry was then transferred to a three-gallon stainless steel autoclave and heated to 200 C. under autogenous pressure. When that temperature was reached the heat was cut off and the autoclave allowed to cool to room temperature. The heating required about 2.5 hours.

The water content of the alcohol phase of the slurry in the autoclave, at the end of the treatment, was about The slurry was filtered and the filter cake dried at 75 C. in a vacuum oven for about 24 hours.

The dried material was a fiutfy white powder. organophilic and hydrophobic. area of 293 MP/ g. It showed no adsorption of methyl red dye. The bulk density of the estersil product was 0.134 g./cc. under a compressive load of 3 p. s. i. Analysis showed that the product contained 87.67% SiOz and 6.56% carbon. After heating the sample at 500 C. to remove the ester coating, the specific surface area of the substrate was found to be 335 M. g. From this It was It had a specific surface value it was calculated that the original estersil had 280 butoxy groups per square millimicrons of substrate surface.

A grease was prepared using the estersil obtained above by mixing the estersil with a Mid-Continent solventtreated petroleum oil (viscosity 300 SUS as 100 F. viscosity index=100) in an oil-estersil weight ratio of 7.5--that is, the mixture contained 13.3% of estersil by weight.

The estersil was initially worked into the oil using a mortar and pestle until a fairly homogeneous mixture was obtained. The mix was then passed thru a Kent three roll ink mill with the rolls set for clearance of 0.0015 inch. Seven passes thru the mill were made to insure complete mixing and give a homogeneous product. The

13 grease obtained was clear and buttery. Its consistency Was equivalent to about a No. 2 to No. 3 grade cup grease. It had a micropenetntion value of 89 at 77 F as measured by the ASTM micropenetration method (ASTM Bulletin No. 147, August 1947, pages 8185).

100% relative humidity, as previously described. After exposure it was found that there was no corrosion of the test panel within inch from the edge of the panel or from the point of support, apparently because the hardening and mud-cracking phenomena had been minimized After five oays storage at 210 to 220 F. and subsethrough proper control of rheological properties. Slnce quent cooling to 77 F. the grease exhibited definite gelit is conventional practice in this corrosion test to ignore ation and had a worked micropenetration of 94. A corrosion within A3 of the edge of the test panel because sandblasted mild steel test panel was coated with a 3 of discrepancies in coating, rust prevention was considto /3 layer of the above grease, placed in a wooden rack, ered excellent. and exposed at 100% relative humidity 120 F. for 150 E l 2 hours. Thereupon inspection showed that the grease had v hardened appreciably and some mud-cracking had o An estersil-thickened grease was made exactly as in curred near the point of support which allowed Water Example 1 p that the amount Y to undercut the grease layer and cause corrosion in an l Was Increased 10 10% y WF g based the area which extended up to 1 f the point f support. weight of grease. After the composition had been mllled Since the rest f the panel was completely protected, a on an ink mill the m1cropenetrat1on at 77 F. was 67. rating f f i to good was i d to hi grease After storage at 210 to 220 F. for ten days the worked Control of the rheological properties of a grease premlcfopenetratlol} at Was EXPosure of test pared in an identical manner was effected by adding a P311615 Coated Wlth a layer of the grease 150 at hydmgenbmding donor d 1 water a temperature of 120 F. and a relative hunudity of The water was added in the proportion of 0.2% by weight 10 0% ShOWed that excellent rust Preventlon was based on the weight of grease and replaced 0.2% of the ta1nedmineral oil, the estersil concentration thus remaining Examplesfi to 17 constant. After adding the water the grease was ink 26 milled and the micro-penetration at 77 F. was ascer- In a manner slrnilar to Examples 1 and 2 greases were tained to be 78. made up with the same oil and the estersil in the same pro- After 10 days storage at 210 to 220 F. the general portions but using various proportions of hydrogen-bondappearance of the grease was excellent and the worked ing donor compounds other than Water as the rheological micropenetration after cooling to 77 F. was 69. The control agents and the properties of such greases were above data indicates the improvement in thickening efiisimilarly evaluated. These examples are shown in the fol ciency afiorded by the addition of the water and the stalowing tabulation. For convenience of reference the rebility of the resultant grease to changes in permanent sults of Examples 1 and 2 have been included in this consistency upon elevated temperature storage. tabulation.

Worked Mieropenetration and Gel Rating Percent Initial at 77 F. after storage at 210-220 F. for Example Hydrogen-bonding Donor Bonder Worked Mi- Days Indicated Rust Prevention No. Compound on cropenetra- 'lest Rating Grease tion at 77 F.

Micropen Gel Rating Days Definite Gelation 5 FairGood. do 10 Excellent. do 10 Do. I. Mmzofnnctio'nal Alcohols 3 Oetyl alcohol 3.3 Slight gelation 4 FairGood. 4. Stearyl alcohoL. 0. 17 Very slight gelatiom 2 Do. 5 d0 1.7 Nogelatlon 2 Do. Hydroabietyl alcohol 2.4 do .c 12 Do.

II. Pelt/functional Alcohols 1,3 propanediol Definite gelation 10 Excellent. Glycerine do. 9 Do. Mannitol a 4 Good. III. Mlmofmictirmal Amines 10 Dodeeyl amine 3.1 221 155 do 8 Excellent. 11 Oetadeeyl amine 4.5 Semi-fluid... Semi-fluid No gelation 8 IV. Diamines 12 Decamethylene Diarnine.. 0.17 74 73. Definite gelation 8 Good. 13 do 8.5 3 -do 10 Excellent altho grease structure separated. V. Ethers v 14 Din-butyl ether 3.6 97 61 .2 Very slight gelation 28 Good.

VI. Esters 15 Trieresyl phosphate 3.3 do 8 Do. 16 Tributyl phosphate 1.7 No gelation 7 Do.

VII. Difunctional Carbon/lie Acids 17 Suceinic acid 0.10 77 57 Definite gelation 10 Do.

The control of rheological properties was further demonstrated by the fact that the grease as a layer had a protective effect against corrosion of sand-blasted mild steel panels. Thus a coating of the grease ,1 to thick was placed on a clean, mild steel test panel and the panel .was subjected to exposure for 150 hours at 120 F. and

All of the products of the foregoing examples showed good lubricating properties. They showed no signs of significant bleeding, or silica separation upon elevated temperature storage. They were all smooth, uniform, homogeneous, unctuous compositions.

The various types of rheological control obtained by the addition of the hydrogen-bonding donor compounds will be seen from the foregoing table. Thus, water and the polyfunctional additives increased the thickening efiiciency of the estersil and therefore tended to preharden the grease with a resultant improvement in rust prevention properties. The monofunctional additives such as the monoamines and monoalcohols tended to reduce the thickening eificiency of the estersil and thereby demonstrated their probable effectiveness for preparing stable dispersions of the estersils at low concentrations in lubricating oils or hydraulic fluids. The relatively weak hydrogenbonding agents such as the ethers and esters reduced grease gelation at elevated temperature and thus improved lubricating properties in the types of anti-friction bearings where feeding characteristics are of prime importance.

Certain of the foregoing observations are more clearly illustrated in Examples 18 and 19 which follow.

Example 18 The following components were weighted and blended with a spatula and then pre-mixed with a mortar and pestle and were finally passed seven times through a Kent 3-roll (14-inch by 10-inch roll) ink mill, with the rolls set for a clearance of 0.0015 inch: 20 grams of the estersil prepared as described in Example 1: 3 grams of stearyl alcohol; 130 grams of a Mid-Continent solvent-treated petroleum oil having a parafiinic base [viscosity 300 S. U. S. at 100 F., viscosity index (V. I.) =100l. The product was a clear, homogeneous, buttery grease. The consistency of the grease was 246 as determined by the micropenetration method at 77 F. The grease was stored in an oven at 220 F. for 2 Weeks and was then removed and worked with a spatula until a fluid material was obtained. The fluid was then diluted by addition of the Mid-Continent solvent-treated petroleum oil used above, and mixed by warming to 140150 F., and agitating with a small mechanical stirrer. In this way, oils containing 2% and 5% of the estersil by weight were prepared.

The oils containing esterified silica were centrifuged at 1600 r. p. m. for 2 hours, using a centrifuge with -inch arms, and the clear oil was decanted from trace amounts of residue. The resulting oils were filtered through a medium-coarse grade sintered glass funnel, all of the material passing through. The viscosity of the oils were measured in the Saybolt viscosimeter and showed the following results:

Percent Estersil 3x33? oejltistgikes V. I

Thus, very small amounts of estersil, well dispersed in the oil by the addition of stearyl alcohol, markedly improved the viscosity index of the oil. The estersil did not separate or settle out, after storage at room temperature for several weeks. If an attempt is made to prepare dispersions in the above-described manner without the addition of stearyl alcohol, relatively rapid settling of the estersil phase will occur.

Example 19 one-half horsepower 400 R. P. M. Lightnin mixer driviug a 10" diameter, 3-bladed propeller. The silicate was heated to a temperature of 35:2 C. by steam injection. A sufiicient amount (about 162 pounds) of a solution containing 2.40% H2504 was added uniformly over a period of about 30 minutes to bring the pH to 9.7i0.2 as measured at 25 C. During this period, the temperature of the reacting mass was maintained below 40 C. The amount of acid added during this step of the process was equivalent to about of the NazO in the original sodium silicate. The sodium ion content remained below 0.3 throughout the process. The clear sol thus obtained, containing tiny discrete particles of colloidal silica less than about 5 in, average diameter, was heated to C. for about 15 minutes.

Solutions of sodium silicate and sulfuric acid were then added simultaneously at a uniform rate over a period of 2 hours through inlets located close to the vortex formed by the agitator. Eighty-five and four-tenths pounds of the sodium silicate solution were used, which contained 13.22 grams of SiOz per milliliters of solution and had a molar SiOzzNazO ratio of 3.25:1. The sulfuric acid was 4.65% aqueous solution and was added in an amount to maintain the pH of the reaction mixture at 10.3 :2 at 25 C. throughout the course of the reaction. Such an amount is sufficient to neutralize about 80% of the NazO in the silicate solution and maintain the sodium ion concentration below 0.3 normal throughout the process. The temperature was maintained at 95 C. throughout the addition of acid and silicate.

During the heating of the heel and the subsequent addition of silicate and acid, the tiny, discrete particles of the heel increased in size and then became chemically bound together in the form of open networks or coherent aggregates of supercolloidal size wherein the colloidal particles are present as dense ultimate units. The aggregates are precipitated.

Still maintaining a temperature of 95 C., the pH of the solution was adjusted from 10.3 to 5.0 by adding 4.65% sulfuric acid at a rate of about 0.24 gallon per minute for 20 minutes and then adding small portions followed by repeated pH determinations until the pH was 5 at 25 C. This required about 32 pounds of the sulfuric acid solution.

The slurry thus obtained was then maintained at 85-95 C. without agitation for from four to sixteen hours in order to coagulate the precipitate to aid in filtra tion. The precipitate was filtered in several portions on a 50-gallon Nutsch, using nylon cloth as a filter medium. The filter cake was washed on the filter with 5 displacements of cold water, and then sucked as dry as possible. The final filter cake contained between 6 and 7% solids.

The washed filter cakes were then combined and sufiicient normal butanol was slurried with the wet cake to give a normal butanol-water azeotrope plus sufficient excess butanol to leave a slurry containing 9 to 10% solids after complete water removal. This mix was then charged to a still for azeotropic dehydration. The still consisted of a 75-gallon reboiler, a 20, 6" diameter column packed with /z Raschig rings, an overhead condenser, and a decanter which returned the butanol-rich upper layer to the column as reflux and separated the heavier waterrich layer. The slurry was then dehydrated azeotropically until the water content of the slurry was below 0.1% by Fischer analysis, and actually around 0.05%.

The butanol slurry was then transferred in 2022# portions to a 4-gallon nickel stirred autoclave and heated to 295305 C. under autogenous pressure. The heat-up required about 3 hours. The temperature was then maintained at 295305 C. for 15-20 minutes and cooled rapidly to below 100 C. over 1530 minutes.

The slurry was removed from the autoclave and dried in a vacuum oven at C. and 10-20 mm. Hg pressure until the silica reached constant weight. Three separate precipitation and azeotropic dehydration batches were prepared as above described and esterified in the auto clave in 25 separate batches. All of the resultant material was then blended to give a homogeneous sample which was a fluffy white powder and was organophilic and hydrophobic. It had a specific surface area of 264 m. g. Analysis showed that the product contained 7.8% carbon. The total non-siliceous ash content was 1.62%.

A water-resistant grease was prepared as follows:

Eleven parts by weight of the above hydrophobic estersil were weighted in a beaker, and 87 parts by weight of a Mid-Continent solvent extracted petroleum oil having a viscosity of 2300 Saybolt Universal seconds at 100 F. into which had been dissolved 0.5 part by weight of Ortholeum 300, an antioxidant consisting of a mixture of complex organic amines, was then added to the hydrophobic estersil and the two were premixed as well as possible with the aid of a spatula. Tricresyl phosphate (1.5 parts by weight) was added and the premixing was continued. The premix was then passed through a Kent 3-ro1l ink mill (roll diameter 4"), seven times with the rolls set at 0.00015 inch clearance. A clear lubricating grease was thus obtained which had a micropenetration of 105 at 77 F. The grease exhibited very good water resistance and had excellent temperature stability.

The water-resistant grease was tested as a lubricant for spherangular bearings under high axial load as follows:

The various parts of a new bearing comprising an outer race about 3 inches in diameter, an inner race, a metal cage, and the spherangular rollers were carefully cleaned with a chlorinated solvent to remove the protective oil film, rinsed with acetone, air dried, and were then accurately weighed on an analytical balance. Each of the parts was greased with a portion of the grease prepared as described above, and the parts were assembled. The outer race was supported in a sleeve in a stationary housing and the inner race was press fitted onto a shaft. The entire bearing was then packed with the grease and assembly was completed. Suitable shields were employed to hold the grease in the bearing chamber. The housing was so constructed that two bearings could be mounted on the same shaft and tested simultaneously. Small holes drilled through the housing permitted thermocouples to be placed in contact with sleeves holding the outer races to measure the approximate bulk temperature of the bearing during operation. Temperatures were recorded continuously and automatically. The shaft was rotated at about 600- 625 R. P. M. An axial load was applied to the sleeve holding the outer race of the rear bearing (i. e., the force was applied to the bearing farthest from the drive end in a direction parallel to the axis of rotation of the shaft) by means of a calibrated spring. The load was increased up to 2000 lbs. in increments of 500 lbs., the load being maintained at a given point only until the temperature appeared to stop rising. The load was maintained at 2000 lbs. until equilibrium conditions were reached, the equilibrium bearing temperature being 205 F. The load was then increased to 2500 lbs., the equilibrium temperature being about 201 F. The hearings were operated at 2500 lbs. axial load for 460 hours. The run was then stopped and the apparatus disassembled. The grease appeared in good condition. A sticky film of oil remained on the rollers and races. The rollers, races, and the cage were again cleaned and reweighed. The total weight loss of the bearings was 4 and 6 milligrams respectively. This exceedingly small amount of wear was barely visible, the original machine marks on the bearing surfaces appearing substantially unchanged, and the bearings therefore remaining in excellent condition.

For comparison, a conventional soda base wheel bearing grease normally used to lubricate bearings of the same general type as employed in this test had a micropenetration of 78 at 77 F. making it thicker and somwhat more difiicult to apply than the grease containing the estersil; it operated at an equilibrium temperature of 214 F. under a load of 2500 lbs; after only 7 hours operation at 2500 lbs. the total weight loss of the bearings was 44.8 and 32.8 milligrams respectively. This shows that the wear observed in extended operation with the esterified silica grease compares most favorably with that resulting from the use of soap grease.

The effect of the additive, tricresyl phosphate, is demonstrated by comparison with a run in which this additive was absent. Thus, a grease was prepared using 12% of the same esterified silica described above in the same oil described above. The grease also contained 5% Ortholeum 300 antioxidant. The micropenetration of the resulting grease was 107 at 77 F. When this grease was used to lubricate the bearings in the manner already described, the equilibrium temperature at a load of 2000 lbs. rose above 293 F. and the test failed after 2 hours at 2000 lbs. When the bearings were disassembled it was found that the grease had failed to feed properly and the tips of the rollers were dry. The total weight loss of the bearings was 9.6 and 11.1 milligrams respectively. Thus the remarkable effectiveness of tricresyl phosphate in transforming an estersil grease, of itself unsuitable for use in this particular application, to one which excels in this very difficult test, has been demonstrated.

I claim:

1. A lubricating composition comprising a major proportion of a mixture of a water-insoluble lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate having a surface of silica and having a specific surface area of from 1 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and a hydrogen bonding donor compound in which every electron donor atom is attached by at least one primary valence bond to an element other than silicon, the proportion of donor compound in the composition being about from 0.1 to 8.5 per cent by weight.

2. A lubricating composition comprising a major proportion of a mixture of a water-insoluble lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with -OR groups, the substrate having a surface of silica and hav ing a specific surface area of from 1 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and a compound selected from the group consisting of water, alcohols, amines, carboxylic acids and their salts, carboxylic esters, carboxylic amides, esters of phosphorus acids, oxyand thioethers, and ketones, the proportion of said donor compound in the composition being about from 0.1 to 8.5 per cent by weight.

3. A lubricating composition comprising a major proportion of a mixture of a hydrocarbon lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate having a surface of silica and having a specific surface area of from 1 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and a hydrogen bonding donor compound in which every electron donor atom is attached by at least one primary 19 valence bond to an element other than silicon, the proportion of donor compound in the composition being about from 0.1 to 8.5 per cent by weight.

4. A lubricating composition comprising a major proportion of a mixture of a hydrocarbon lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate being amorphous silica having a specific surface area of from 200 to 900 square meters per gram, the coating of OR groups bein chemically bound to said silica in the proportion of at least 270 groups per 100 square millimicrons of substrate surface area, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and said substrate being porous and having an average pore diameter of at least 4 millimicrons, and the lubricating composition comprising further about from 0.1 to 8.5 per cent by weight of a compound selected from the group consisting of water, alcohols, amines, carboxylic acids and their salts, carboxylic esters, carboxylic amides, esters of phosphorus acids, oxyand thio-eth-ers, and ketones.

5. A lubricating composition comprising a major proportion of a mixture of a hydrocarbon lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate being amorphous silica having a specific surface area of from 200 to 900 square meters per gram, the coating of --OR groups being chemically bound to said silica in the proportion of at least 270 groups per 100 square millimicrons of substrate surface area, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and said substrate being porous and having an average pore diameter of at least 4 millimicrons, and the lubricating composition comprising further about from 0.1 to 8.5 per cent by weight of water.

6. A lubricating composition comprising a major proportion of a mixture of a hydrocarbon lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate being amorphous silica having a specific surface area of from 200 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica in the proportion of at least 270 groups per 100 square millimicrons of substrate surface area, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and said substrate being porous and having an average pore diameter of at least 4 millimicrons, and the lubricating composition comprising further about from 0.1 to 8.5 per cent by weight of an ester of a phosphorus oxy-acid.

7. A lubricating composition comprising a major proportion of a mixture of a hydrocarbon lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate being amorphous silica having a specific surface area of from 200 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica in the proportion of at least 270 groups per 100 square millimicrons of substrate surface area, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and said substrate being porous and having an average pore diameter of at least 4 millimicrons, and the lubricating composition comprising further about from 0.1 to 8.5 per cent by weight of an amine.

8. A lubricating composition comprising a major pro portion of a mixture of a hydrocarbon lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate being amorphous silica having a specific surface area of from 200 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica in the proportion of at least 270 groups per square millimicrons of substrate surface area, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and said substrate being porous and having an average pore diameter of at least 4 millimicrons, and the lubricating composition comprising further about from 0.1 to 8.5 per cent by weight of a monofunctional compound selected from the group consisting of water, alcohols, amines, carboxylic acids and their salts, carboxylic esters, carboxylic amides, esters of phosphorus acids, oxyand thio-ethers, and ketones.

9. A lubricating composition comprising a major proportion of a mixture of a hydrocarbon lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with -OR groups, the substrate being amorphous silica having a specific surface area of from 200 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica in the proportion of at least 270 groups per 100 square millimicrons of substrate surface area, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, and said substrate being porous and having an average pore diameter of at least 4 millimicrons, and the lubricating composition comprising further about from 0.1 to 8.5 per cent by weight of a polyfunctional compound selected from the group consisting of alcohols, amines, carboxylic acids and their salts, carboxylic esters, carboxylic amides, esters of phosphorus acids, oxyand thio-ethers, and ketones.

10. A grease composition comprising a major proportion of a Water-insoluble lubricating oil and a solid which is organophilic, being preferentially wetted by butanol in a butanol-water mixture, said solid comprising a supercolloidal substrate coated with OR groups, the substrate having a surface of silica and having a specific surface area of from 1 to 900 square meters per gram, the coating of OR groups being chemically bound to said silica, R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon atom attached to oxygen is also attached to hydrogen, said solid being present in an amount suflicient to thicken the oil to a grease consistency, and a compound selected from the group consisting of water, alcohols, amines, carboxylic acids and their salts, carboxylic esters, carboxylic amides, esters of phosphorus acids, oxyand thio-ethers, and ketones, the proportion of said compound in the composition being about from 0.1 to 8.5 per cent by weight.

References Cited in the file of this patent UNITED STATES IATENTS 2,554,222 Stross May 22, 1951 2,573,650 Peterson Oct. 30, 1951 2,614,079 Moore Oct. 14, 1952 2,629,691 Peterson Feb. 24, 1953 2,647,872 Peterson Aug. 4, 1953 2,652,361 Woods et al. Sept. 15, 1953 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR PROPORTION OF A MIXTURE OF A WATER-INSOLUBLE LUBRICATING OIL AND A SOLID WHICH IS ORGANOPHILIC, BEING PERFERENTIALLY WETTED BY BUTANOL IN A BUTANOL-WATER MIXTURE, SAID SOLID COMPRISING A SUPERCOLLOIDAL SUBSTRATE COATED WITH -OR GROUPS, THE SUBSTRATE HAVING A SURFACE OF SILICA AND HAVING A SPECIFIC SURFACE AREA OF FROM 1 TO 900 SQUARE METERS PER GRAM, THE COATING OF -OR GROUPS BEING CHEMICALLY BOUND TO SAID SILICA, R BEING A HYDROCARBON RADICAL OF FROM 2 TO 18 CARBON ATOMS WHEREIN THE CARBON ATOM ATTACHED TO OXYGEN IS ALSO ATTACHED TO HYDROGEN, AND A HYDROGEN BONDING DONOR COMPOUND IN WHICH EVERY ELECTRON DONOR ATOM IS ATTACHED BY AT LEAST ONE PRIMARY VALENCE BOND TO AN ELEMENT OTHER THAN SILICON, THE PROPORTION OF DONOR COMPOUND IN THE COMPOSITION BEING ABOUT FROM 0.1 TO 8.5 PER CENT BY WEIGHT. 